Prompt Mastery Intermediate

# Bad
> fix the bug

# Good
> In src/utils/date.ts, the formatDate function returns "Invalid Date" when passed
> a Unix timestamp in seconds (e.g., 1700000000). It expects milliseconds. Fix it
> to handle both seconds and milliseconds. Add a test case to tests/utils/date.test.ts.

# Bad
> add pagination

# Good
> Add cursor-based pagination to the GET /api/posts endpoint in src/routes/posts.ts.
> Follow the same pattern used in src/routes/comments.ts. The response should include
> nextCursor and hasMore fields. Update the PostRepository in src/repos/post.repo.ts
> to accept cursor and limit parameters. Default limit: 20, max: 100.

# Bad
> clean up the code

# Good
> Refactor src/services/payment.ts to extract the Stripe-specific logic into
> a separate src/services/stripe.adapter.ts file. Create a PaymentProvider
> interface so we can swap Stripe for another provider later. Keep all existing
> tests passing.

> Write comprehensive unit tests for src/services/user.service.ts using Jest.
> Cover: createUser (valid input, duplicate email, missing fields),
> updateUser (partial update, non-existent user), deleteUser (soft delete behavior).
> Mock the UserRepository. Follow the test style in tests/services/auth.service.test.ts.

> Review the changes in the last commit (git diff HEAD~1). Focus on:
> 1. Security issues (SQL injection, XSS, auth bypasses)
> 2. Performance problems (N+1 queries, missing indexes)
> 3. Error handling gaps
> Do NOT suggest style changes. Only flag real bugs and security issues.

> Add JSDoc comments to all exported functions in src/utils/. Include @param
> and @returns tags with types. For complex functions, add a @example block.
> Don't add comments to internal/private functions.

> Migrate all API route handlers in src/routes/ from Express to Fastify.
> Start with src/routes/auth.ts as a reference. Keep the same URL paths and
> HTTP methods. Use Fastify's schema validation instead of our custom middleware.
> Do one file at a time and run tests after each.

> Review the git log for the past week. Create a changelog grouped by:
> Features, Bug Fixes, and Improvements. Use the conventional commits format.
> Skip merge commits and CI-related commits.

> The /api/dashboard endpoint in src/routes/dashboard.ts takes 3 seconds to load.
> It makes 5 sequential database queries. Optimize it by:
> 1. Running independent queries in parallel with Promise.all
> 2. Adding caching for the stats query (5 minute TTL)
> 3. Adding a database index if needed for the slow queries

> Add comprehensive error handling to src/services/payment.ts:
> - Wrap all Stripe API calls in try/catch
> - Create custom error classes in src/errors/ (PaymentFailedError, CardDeclinedError)
> - Log errors with context (userId, amount, stripe error code)
> - Return user-friendly error messages (don't expose Stripe internals)

# 11. Type Safety
> Add TypeScript types to all 'any' types in src/services/. Use strict types, no 'any'.

# 12. API Endpoint
> Create a new POST /api/webhooks/stripe endpoint following the pattern in src/routes/webhooks/github.ts

# 13. Database Query
> The query in src/repos/analytics.ts line 34 is slow. Add an index and optimize the JOIN.

# 14. Configuration
> Add environment variable validation at startup in src/config.ts. Fail fast if required vars are missing.

# 15. Cleanup
> Find and remove all unused imports and dead code in src/utils/. Run tests to make sure nothing breaks.